An aircraft which uses wheels for taking off and landing typically employs hydraulic brakes to control movement of the wheels, i.e., to stop the wheels from rotating. A typical hydraulic brake for an aircraft includes a hydraulic fluid source, a hydraulic actuator coupled to a wheel, and tubing which connects the hydraulic fluid source to the hydraulic actuator.
To apply the brake, a pilot of the aircraft increases the pressure of the hydraulic fluid from the hydraulic fluid source. As the pressure increases, the hydraulic actuator applies force to a brake element which pushes against the wheel. Friction between the wheel and the brake element (e.g., a pressure puck which is capable of withstanding high temperature) stops the wheel if the wheel is turning, and prevents the wheel from rotating further.
Some conventional hydraulic brakes have a relatively tight design which minimizes pressure loss thus enabling the pilot to maintain hydraulic pressure in the brake system even after power to the aircraft is turned off, and thus maintain application of the hydraulic brakes for several hours. With the ability to maintain brake pressure, the pilot is capable of using the hydraulic brakes as parking brakes to prevent the aircraft from substantially moving (e.g., drifting from a parked location) thus alleviating the need for other parking mechanisms (e.g., wheel blocks, tie downs, etc.) during this period. The use of stored hydraulic pressure for aircraft parking brakes is superior to conventional electric brakes for aircraft which require sustained electric current to hold the brake elements against the wheels and thus continuously consume power while the electric brakes remain on.